Devices for selectively detecting specific wavelength components of a light beam have been used in practice for quite some time, reference being made, just as an example, to German Patent Application DE 101 02 033 A1. FIG. 2 there shows a device, in which a light beam to be detected is spectrally split by a prism. A selection device in the form of a slit diaphragm is located downstream of the prism. Certain wavelength components are blocked by the slit diaphragm jaw while other wavelength components pass through the slit diaphragm and are detected in a first detector, while still other wavelength components are reflected by the slit diaphragm jaw by a totally reflecting coating and are then detected in a second detector. Having a multitude of components, this system is extremely complex and in addition not very flexible in terms of a changed composition of the spectral regions to be detected.
Methods for suppressing excitation lines in the detection light beam of a microscope are also used in practice. In the known methods, the excitation lines are generally blocked using special filters, for example, electro-optical filters, that have an absorbing effect for the wavelengths of the excitation lines. In this connection, it is a disadvantage that the absorption is generally not complete so that in spite of the filtering, there is still excitation light hitting the detector. This is problematic especially when the intensity of the excitation line is many times greater than the intensity of the actual detection light, which is typically the case in fluorescence microscopy. A further disadvantage is that the filtering generally also affects the detection light, thus corrupting the measurement result.